Hydrofoil system and method of forming lift foils for use therein



Dec. 12, 1967 D. WRAY, JR 3,357,389

HYDRGFOIL SYSTEM AND METHOD OF FORMING LIFT FOILS FOR USE THEREIN F I B E 2 fi I3Z- w S '28 .-1Z6 3 z k 134 I 81 3 14 2o INVENTOR DAVID WRAY, JR.

AITORNEY D. WRAY. JR SYSTEM AND METHOD OF FORM Dec, 12, 1967 ING HYDROFOIL LIFT FOILS FOR USE THEREIN Filed June 28, 1965 4 Sheets-Sheet F'IB INVENTOR DAVID WRAY,JR.

I BY Afi d ATI'ORNEY Dec. 12, 1967 D. WRAY, JR 3,357,389

HYDROYOIL SYSTEM AND METHOD OF FORMING LIFT FOILS FOR USE THEREIN Filed June 28, 1965 4 Sheets-Sheet R F'II3 IE|' INVENTOR DAVID WRAY, JR.

A'ITORNEY D. HYDROFOIL SYSTEM AND METHOD OF FORMING LIFT FOILS FOR USE THEREIN Filed June 28, 1965 4 Sheets-$heet 4 FIG 7 STRUT 2.

F'II3 EI C2 96 HYDROFOIL was w... 100

I F I l3 E EXTRUSION 90 INVENTOR DAVID WRAY, JR.

BY A/tu ATI'ORNEY United States Patent Ofiice 3,357,389 Patented Dec. 4 12, 1 967 HYDROFOIL SYSTEMAND METHOD QEFORM- g ING LIFT FQILS FOR .USE THEREIN David Wray, In, Los Gatos, Cal ill, assignor to,FMC Crporation, San Jose, Calif, a corporation of, Delaware Filed June 28 1965, Set. No. 46,7,218 16 Claims. (Cl. 114- 665) The present invention pertains to hydrofoil s, and more particularly relates to a structural arrangement of hydrofoils which achieves improved Operation resulting in high stability and efficiency, and to a method of forming the hydrofoil lift surfaces used in the structure.

In general terms, the present invention provides retractable forward hydrofoil units which provide wide stance support to a hull and are movable inward from their flying positions to inoperative positions lying laterally inward and below the longitudinal edges of the hull. The invention employs base-vented hydrofoil blades and includes a method of producing the same, and a novel venting arrangement that supplies atmospheric air to the hydrofoil blades along their struts to prevent destructive cavitation. Further, the hydrofoil units are constructed and arranged to minimize fouling of the lift surfaces, to minimizes accidental damage to the foils when the hull is drawn up to a dock or the like, to reduce the operating hazards of projecting and retracting the hydrofoils, and to obviate the use of deck space normally required to store that type of hydrofoil which is retracted upward over the hull.

One of the objects of the present invention is to provide a retractable hydrofoil arrangement having improved operating characteristics.

Another object is to provide an improved venting system for preventing destructive cavitation and excessive pressure drag along a surface-piercing hydrofoil.

Another object is to provide hydrofoil structure which provides wide-stance support for a hull and retracts downwardly and inwardly so as to effectively shield the foils in their retracted positions from lateral obstacles past which the hull must travel.

A further object is to provide a hydrofoil-equipped hull which does not require deck space for the hydrofoils or their mounting and actuating structure.

A further object is the provision of improved surfacepiercing, area stabilizing hydrofoils achieved by particular structural arrangements which inhibit fouling of the lift surfaces.

Another object is to provide a hydrofoil system wherein the aft hydrofoil is intermittently surface-piercing and area stabilized.

A further object is the provision of a hydrofoil system wherein braces for the lift blades both fore and aft provide secondary lifting surfaces when the hull is operated in following seas that submerge the hydrofoils and engulf the braces.

Other objects and advantages of the hydrofoil structure of the present invention will become evident from the following description and from the accompanying drawings, wherein:

FIGURE 1 is a front elevation, partly broken away, of a hull and hydrofoil arrangement according to the present invention, the hydrofoil units being in their operative or flying position supporting the hull above the surface of the water.

FIGURE 2 is a side elevation of the hull and hydrofoil unit arrangement shown in FIGURE 1. 7

FIGURE 3 is an enlarged fragmentary elevation with parts broken away, including one forward hydrofoil unit, the view being taken along lines 33 on 2.

FIGURE 4 is a side elevation, with parts broken away,

of the hydrofoil unit shown in FIGURE 3, the view being taken as indicated by the lines 44 on FIGURE 3.

FIGURE 5 is a plan of the hydrofoil unit shown in FIGURE 4.

FIGURE 6 is an enlarged fragmentary section, taken along lines 6 6 on FIGURE 3, showing the actuating mechanism for retracting and projecting the starboard hydrofoil unit.

FIGURE 7 is an enlarged transverse section of a typical strut meinb'er used with both the fore and aft hydrofoil units illustrated in FIGURE 1.

FIGURE 8 is an enlarged transverse section of a typical hydrofoil blade used in the hydrofoil units shown in FIGURE 1.

FIGURE 9 is a schematic plan of the basic ,foil extrusion used to form the figure 8 and other hydrofoil blades.

FIGURE 10 is an enlarged transverse section of the brace which interconnects the hydrofoil blade and strut of the forward hydrofoil units, and is also employed in the aft hydrofoil unit.

The hydrofoil system of the present invention includes a displacement type hull H, FIGURES 1 and 2, which is powered by an inboard engine, not shown. The engine drives a propeller shaft 12 which is coupled .to a propeller 14 that is adapted to propel the loaded hull H at speeds sufficient to develop lift in its hydrofoil lift blades. The hydrofoil lift blades are carried by forward port and starboard hydrofoil units 16 and 18, respectively; and a stern or aft hydrofoil unit 20. When the hull has sufficient forward speed, the hydrofoil units elevate the hull H above the surface W of the water to its flying position in which higher speeds are attained due to the elimination of the resistance normally generated by the hull moving through the Water. 7

Both forward hydrofoil units 16 and 18 are similarly constructed, but of opposite orientation; and the ensuing description is primarily directed to the starboard hydrofoil unit 18; However, the same reference numbers are equally applicable to the port hydrofoil unit 16, and are so used on FIGURE 1. V

The starboard hydrofoil unit 18 (FIGS. 3-6) is pivotally mounted on the hull H by means including two bearings 22 which depend from an elongate mounting plate 24 that is rigidly secured to the hull. The upper end of a support strut 26 has an integral sleeve 27 which rotatably receives a pivot shaft 28 that is rotatably mounted in the bearings 22. The turning axis of the pivot shaft 28 lies in a vertical plane substantially parallel to the longitudinal centerline of the hull H, and in a horizontal plane substantially parallel to the surface W of the water when the hull is in its illustrated flying position.

The hull H (FIGS. 3 and 6) includes bottom planking or covering 30, and similar side planking or covering 32, both the bottom and side planking being reinforced by, and/or secured to, a plurality of transverse bulkheads 34, only one being shown, and a plurality of ribs 36, two of which are shown. In the region of the -strut 26, the bottom planking 30 (FIG; 6) adjacent the rib 36 is apertured to forma chamber 38 that is flooded with water when the hull is floating. Upright walls 40 and 42 (FIG. 3), the rib 36, a wall 44 (FIG. 6) which is parallel to the rib, anda top cover panel 46 (partly broken away in FIG. 6) define the vertical extent of the chamber 38. Water is in part isolated from the interior of the hull by an upwardly sloping wall 48 (FIG. 6) and a similar wall 50, which are respectively located fore and aft of the chamber 38. Wall 40, it will be noted extends between, and is secured to, the r earmost rib 36 and to the bulkhead 34. The outer ends of the walls 48 and 50 are sealed to the W511 no.

At each side of the sealed chamber 38, the walls 48 and 50 provide a downwardly open relieved portion of the hull, as is indicated by the reference numeral 52 (FIG. 3) which designates the aft relief. The relieved portions of the hull, including a portion directly below the chamber 38, provide clearance space to accommodate the upper end portion of the strut 26 when the hydrofoil unit 18 s retracted and the strut 26 occupies its phantom-hue position shown in FIGURE 3.

The hydrofoil unit 18 (FIGS. 3 and 6) is extended and retracted by a double-acting hydraulic ram 54 (FIG. 6) which is pivoted at 56 to a fixed structural member 58. The piston rod 60 of the ram is pivoted at 62 to the free end of a lever arm 64 that is secured to a shaft 66. Shaft 66 is rotatably mounted in a bearing sleeve 68 that is welded to and projects through both ribs 36. Since the forward end of the sleeve 68 lies within the chamber 38, the adjacent end of the shaft 66 is exposed to water when the hull H is floating. In order to assure that the water will not travel along the shaft 66 into the hull, the sleeve and the shaft are provided with a plurality of aligned grooves in which conventional elastomeric O-rings 76 are mounted.

A lever 72 is keyed to the forward end portion of the shaft 66 for swinging movement within the chamber 38. When the piston rod 60 is in its fully extended position, as seen in FIG. 3, the free end of the lever 72 lies on a linear axis 73 which intersects the axis of the shaft 66. Axis 73 also intersects the axis of a pivot pin. 74 on the end portion of the lever 72, and the axis of a pivot pin 76 which is held in a bracket 78 that is secured to the inner surface of the strut 26. A linearly adjustable link 80 interconnects the pivot pins 74 and 76 so that linear alignment of the lever 72 and the link 88 (with reference to the projected position of the hydrofoil unit 18) can be attained when the hydrofoil unit 18 is initially installed and coupled to the hydraulic ram 54. With the lever and link thus aligned, it will be apparent that maximum holding force is attained for resisting inward swinging movement of the hydrofoil unit 18 by minimizing the tendency of the lever and link to buckle.

The fluid connections for the ram 54 and the corresponding connections to the other ram for the port hydrofoil unit 16 (none of which connections are shown) are conventional and are connected in parallel to a source of hydraulic fluid under pressure so that simultaneous projection or retraction of the hydrofoil units 16 and 18 is effected. When the hydrofoil units are retracted, both units assume positions underlying the hull H, as is shown in phantom lines for the hydrofoil unit 18 (FIG. 3) and the lever 72 and link 80 of each unit folds upward into the chamber 38. The strut 26 has its upper end portion thus disposed in'the relieved portions (as at 52, FIG. 3,) of the hull, and the lateral extremity of each hydrofoil unit lies well inward of the plan profile of the hull so that both hydrofoil units are protected during docking or close maneuvering of the hull. I

The hydrofoil unit 18 (FIGS. 3-5) includes an elongate, swept back main hydrofoil blade 82 that is secured to the lower end of the strut 26 and extends outward therefrom in piercing relation to the surface W of the water when the hull H is flying. The main blade 82 is joined, as by welding, to a swept back tip foil blade 86 which extends inward from the lower end of strut 26 in nonplanar relation to the main hydrofoil blade 82. It will be seen in FIGURE 1 that the tip foil 86 has less positive dihedral than the main blade 82, the purpose of which will be later described. A brace 84, also swept back, interconnects the outer end of the main hydrofoil blade 82 with the upper end portion of the strut 26. FIGURE illustrates the cross sectional supercavitating shape of the brace 84, reference to which is later made in this description.

A particular feature of the main blade 82 and the tip foil 86 is the manner in which they are formed from an extruded form 88 (FIG. 9) which has constant camber,

whereby the completed main blade and tip foil blade have both an inconstant camber and a varying angle of attack without resorting to twisting or machining the blades as has been formerly done. So formed, the main blade and the tip foil are more accurate than twisted blades, are more easily constructed than blades which must be machined to achieve the same result, and may possibly be stronger than a twisted blade, depending upon how severely a twisted blade must be bent and rebent until it has the desired camber and attack angle variation along its length.

The extrusion 88 (FIG. 9) has the well known baseventilated wedge shaped cross section shown in FIGURE 8, with a thin leading edge 9% and a blunt trailing edge 92. As clearly shown in FIGURE 5, the main hydrofoil blade 82 is tapered from its outer extremity where it joins the brace 84, to the point where it joins the strut 26. The trailing edge 92 of the tapered main hydrofoil blade 82 corresponds to the phantom line 92 on FIGURE 9. The main hydrofoil blade 82 is formed by cutting or milling the extrusion 88 along the phantom line 92, whereby a narrow end 88A of the blade is defined between the leading edge (FIG. 8) and a reference point 96 at the juncture of the phantom line 92 and the end 94. By this simple procedure, the thus formed main hydrofoil blade has a uniformly changing camber (and geometrical angle of attack when installed) along its length by reason of the following facts:

The full width end 88B of the extrusion 88 corresponds to the portion between the leading and trailing edges 90 and 92, respectively, FIGURE 8, and the camber of that end of the extrusion can be measured along perpendicular lines that are erected from a chord line C1, which passes through the leading edge 98 and bisects the height of the extrusion along the edge 92, to the points where the perpendiculars intersect the mean camber line 95. A correspending chord line C2 for the narrow end 88A of the extrusion bisects the height of the extrusion along the corner edge at 96, and is thus not coincident with the chord line C1. Therefore, perpendicular measurements from the mean camber line of the main hydrofoil blade 82 relative to the two chord lines C1 and C2 are different, thereby indicating that the camber is less at the small end 88A of the main blade than at the large end 88B. Further, when the blade is installed with a given geometrical angle of attack at its wide end, the angle of attack for the small end of the blade is measurably less. This difference in angle of attack, that is to say the angular differences between an arbitrary fluid velocity vector line V (FIG. 8) and the two chord lines C1 and C2, illustrates the appreciable change in geometrical angle of attack which is attained by tapering the plan profile of the hydrofoil blade extrusion 88; the length of the arc A1 struck from the center A1 and measured between the vector line V and the chord line C1 is seen to be longer than the corresponding arc A2 of the same radius struck from the center A2.

In one hydrofoil installation according to the present invention, the main hydrofoil blades 82 with a cross-sectional shape corresponding to the shape shown substantially in true scale in FIGURE 8 had a length of 36.438 inches, a maximum chord of 12 inches and a minimum chord of 10 inches. So formed, the angular difference in angle of attack between the two blade ends was .83 of a degree. In the same installation, the tip foils 86 were 15.367 inches long, had a maximum chord of 10 inches, a minimum chord of 5 inches, and the angular difference in angle of attack between their ends was 1.75 degrees.

The tapered tip foil blade 86 (FIG. 5) is similarly formed from another extrusion 88 (FIG. 9) by cutting or.

milling the extrusion along the phantom lines 88 and 100 whereby in the same manner the tapered main blade 82 has varying camberv and an inconstant angle of attack, the tapered tip foil blade 86 also has varying camber and an inconstant angle of attack. Since the tip foil blade 86 is quite short and its end chord dimensions are radically different, the edge-on pi'ofile of the tip foil blade as shown in FIGURE 3 exhibits a marked taper toward its narrow end.

The significance of the increased angle of attack of the main hydrofoil blade 82 toward its outer end is that, as is well known in the art, Conditions which tend to submerge the main blade, such as uneven loading of the hull H or centrifugal force during a turn or in following seas, will automatically result in increased lift, as in ordinary surface-piercing hydrofoil blades having constant angle of attack. Unlike ordinary hydrofoil blades, however, the lift force of the present foils increases as a multiple of the degree to which the main hydrofoil blade 82 is submerged because higher lift portions (the increased angle of attack portions) of the blade become submerged. The main hydrofoil blade 82 thus exerts a more powerful than usual righting force that tends to hold the hull on an even keel whenever the hull rolls.

If the lift force of the main hydrofoil blade 82 should stagnate in following sea conditions as the blade follows the crest of a wave and the downward orbital movement of the water particles destroy lift, the tip foil blades 86 will remain deeply submerged and relatively unaffected. It will be noted in FIGURE 1 that an arbitrary force vector V1 normal to and bisecting the submerged portion of the main hydrofoil blade 82 lies below a corresponding force vector V2 normal to the tip foil blade 86, at the points where they intersect a plane V3 coincident with the centerline of the hull H, due to the fact that the main hydrofoil blade and tip foil blade are not coplanar. Accordingly, if the main hydrofoil blade lift force stagnates as mentioned above, the tip foil blade continues to provide powerful lift and righting moment to the hull due to the angular relation of the tip foil 86 to the main hydrofoil blade 82; it will be apparent that if the tip foil blade and main blade were coplanar, a force vector for the tip foil blade would intersect the plane V3 below the deck of the hull and would result in much less righting moment.

If lift should decrease in both the main hydrofoil blade 82 and the tip foil blade 86, as can occur due to fouling such as from kelp draping across the lift surfaces, means are provided to supply auxiliary lift if the hull rolls far enough to submerge the brace 84. For this purpose, the brace 84 (FIG. has a cross-sectional shape approximating the shape of the main hydrofoil blade 82. The brace is formed of a length of uniformly thick, rectangular plate rolled transversely to provide arcuate lower and upper surfaces 162 and 104, respectively. The upper surface 194 of the plate is then milled to form a downwardly, forwardly sloping bevel 196 that terminates at a narrow leading edge 10%, the thus produced brace 84 functioning as a hydrofoil blade and preventing capsizing of the hull if the above described, or similar, conditions reduce lift in the tip foil blade 86 and the main hydrofoil blade 82 to the extent that the brace 84 is submerged.

In regard to the possibility of the tip foil blade 86 and the main hydrofoil blade 82 becoming fouled, it should be here noted that both blades are self-cleaning. For this purpose both the tip foil blade and the main hydrofoil blade, as shown in FIGURE 5, sweep sharply back from their juncture with the strut 26. It will thus be apparent that when the hull is flying, any foreign substance that may drape over either the tip foil blade 86 or the main hydrofoil blade 82 will be washed upward away from the strut 26 in the case of the main blade 82, or downward away from the strut in the case of the tip blade 86. Accordingly, in both instances the foreign substance is immediately removed from the submerged blades before dangerous loss of lift can develop. The above described swept back configuration of the hydrofoil blade 82 and the tip foil 86 is important for another reason which concerns the prevention of destructive cavitation.

A particular feature of the present invention concerns the mode of venting the hydrofoil blade 82 and the tip foil 86 to prevent the detrimental effects of destructive cavitation and pressure drag. The strut 26 (FIG; 7) is symmetrical in cross-section, and thus has no camber, with a pointed leading edge andpartially convex side surfaces 112 that terminate at a blunt trailing edge or base 114. This shape of uncambered strut produces a low pressure void along the blunt trailing edge 114. The same conditions are true of the blunt trailing edges 92, and 98 (FIGS. 8 and 9) for the main hydrofoil blade 82 and the tip foil blade 86, i.e., these blunt edges produce adjacent low pressure voids which tend to cause pressure drag. 1f the void behind the main blade 82 is blocked intermittently by turbulent water, increased pressure drag results which is manifested by a reduction in speed and greater power consumption.

The hydrofoil units 16 and 18 (FIGS. 1 and 5) eliminate this blocking problem by providing a unique system of atmospheric ventilation of the voids initiating downward along the struts 26 and thence in two directions outward to the end of the tip foil blades 86, and outward to the surface of the water along the main hydrofoil blades 82. This mode of venting, as will be presently described, results from the fact that the submerged portion of the strut 26 (FIGS. 3+5) forms a trailing void in the stippled area at 118 (FIG. 4) along the rear edge 114 of the strut 26. Since the rear faces of the strut 26, the blade 82 and the tip foil 86 are joined together at a smooth junction that has no flow-arresting projections, the air flowing into the strut void 118 communicates with the trailing voids at 122 and 124 of the tip foil 86 and the hydrofoil blade 82, respectively, and this flush construction permits smooth flow of the venting air in both lateral directions.

The swept back hydrofoils produce an air-flow component in the direction toward the rearmost end of the foil. Accordingly, air flow propagation in the voids 122 and 124, because of the induced motion imparted to the air flow caused by sweepback, originates at the juncture 129 with atmospheric air that travels down the edge 114 of the uncambered strut 26, and then travels outward along the base of the tip foil blade 86 and the base of the hydrofoil blade 82. Thus, all ventilating air is delivered along the base of the uncambered strut 26.

The turbulence off the end of the tip foil caused by this ventilating air is minimized because the angle of attack and the chord of the tip foil are reduced at the tip, as previously described. This feature produces the well known and desirable elliptical s-panwise lift distribution. In the case of the main hydrofoil blade 82, blocking of the void 124 where the blade pierces the water is prevented because the air flow is upward at that point and diffuses the water spray and sheets that might otherwise be drawn into the void as in conventional venting arrangements where the flow of air originates at this point.

The aft foil unit 20 (FIGS. 1 and 2) includes a central vertical strut 126 initially having the same uhcambered cross sectional shape as the strut 26 (FIG. 7). The strut 126 is provided with a trailing recess in which is mounted a remotely operable steering rudder 128 that extends vertically between a pair of aft foil blades 130 and a pair of braces 132. A propeller bearing 134 on the lower end of the strut rotatably mounts the propeller shaft 12. The aft foil blades 130 are formed in a manner similar to that in which the tip foil blades 86 are formed, and have substantial positive dihedral whereby the foil blades are at least part of the time in piercing relation to the surface of the water so as to achieve area stabilization. Further, the foil blades 130 overlie the propeller 14 so as to inhibit cavitation of the propeller.

The upper end portion of the strut 126 is made laterally rigid by the braces 132, which diverge upward, are connected to the hull H, and have the same supercavitating cross=sectional shape as the braces 84 (FIG. 10). The braces 132 thus serve as auxiliary lift surfaces if following seas cause submergence of the braces such as can happen if the aft foil blades 130 are behind the crest of a wave and lift is impaired by downward orbital movement of the water particles. In such instances, the braces develop auxiliary lift and assist in preventing excessive pitching of the hull. From the foregoing, it will be evident that the aft foil unit 20 is based upon the concept of a lower lift surface which has positive dihedral and intermittently pierces the surface, and an upper, auxiliary liftsurface which also has positive dihedral and is intermittently wetted under certain operating conditions.

In summary, and by way of emphasizing the manner in which the hydrofoil craft of the present invention differentiates from the prior art, the forward hydrofoil units 16 and 18 provide retractable lift surfaces which in flying position ensure a very wide stance support for the hull H to minimize roll of the hull, and yet are adequately protected from lateral obstacles when retracted because they lie inward of the plan profile of the hull. Further, the retracting mechanism and. associated structure is so arranged that only minimal space is required, the elements movable through the hull are easily sealed to prevent the intrusion of water; and the hydrofoil units possess great strength and rigidity without resorting to complex structure. The combined functions of ventilating the forward foils by inducing atmospheric air down the base of the uncambered strut 26, due to the sweep'back of the hydrofoil blade 82 and the tip foil blade 86, and the self-cleaning action of the blades due to their sweepback so that material which might otherwise destroy lift is unable to achieve static positions draped over the lift surfaces, are also important to the invention. The method of forming a varying camber, base ventilated hydrofoil blade from an extrusion having constant camber makes possible low cost, volume production of such elements.

Having thus described my invention, that which is believed to be new, and for which protection by Letters Patent is desired is:

1. A hydrofoil craft comprising a hull including upright side walls, a pivotable hydrofoil unit at each side of the hull, means connected to said hull and defining a pivot I axis for each hydrofoil unit inwardly of said upright side wall, and means for swinging said hydrofoil unit about said axis between an outer position in which said unit has portions projecting outwardly beyond the plan profile of said hull, and an inner position in which said unit lies totally within said plan profile beneath said hull and inward of said side.

2. Hydrofoil craft comprising a hull, a retractable hydrofoil unit pivotally connected to said hull for swinging movement relative to the hull, wall means interiorly of said hull defining a downwardly open chamber, a rotatable power shaft extending through at least one wall of said chamber, articulated linkage movable in said chamber and interconnecting said power shaft and said hydrofoil unit for effecting swinging movement of the hydrofoil unit upon rotation of said power shaft, a sleeve surrounding said power shaft in sealed relation to said one wall, power means for selectively rotating said power shaft, and fluid sealing means interposed between said power shaft and said sleeve to prevent leakage along the shaft into the hull when the hull is floating.

3. Hydrofoil craft comprising a hull, retractable hydrofoil unit pivotally connected to said hull for movement between a retracted position and an extended position, wall means projecting upward into said hull and defining a downwardly open and otherwise closed chamber lying in the plane of movement of said hydrofoil unit, an inboard rotatable power shaft extending through a wall of said chamber, the axis of rotation of said power shaft being substantially normal to said plane, articulated linkage movable in said chamber and interconnecting said power shaft and said hydrofoil unit, a sleeve surrounding said power shaft and sealed to the inboard side of said one 8 wall, power means for selectively rotating said power shaft, and fluid sealing means interposed between said power shaft and said sleeve to prevent leakage into the hull when the hull settles in the water.

4. A hydrofoil system comprising a hull, a pivot shaft mounted on each forward side portion of said hull, a strut depending from said pivot shaft for swinging movement transversely of said hull, a lift foil secured to said strut in swept-back relation thereto, wall means within said hull defining a downwardly open chamber adjacent to and in the plane of swinging movement of said strut, a rotatable power shaft extending through a wall of said chamber, articulated linkage movable in said chamber and interconnecting said power shaft and said strut, power means for selectively rotating said power shaft, and sealing means interposed between said power shaft and said wall for preventing the entry of water into the hull from said chamber when the hull is floating.

5. A retractable hydrofoil system providing wide stance support comprising a hull, port and starboard pivotable struts depending from said hull for transverse movement between retracted positions in which the struts form an acute angle with the bottom of the hull and lie inward of the load water line to extended positions in which the distal end portions of the struts lie outwardly beyond the plan profile of the hull and cooperatively diverge toward the surface of the water when the hull is flying, and a hydrofoil blade carried by each strut and projecting laterally outward and rearward from the strut in piercing relation to the surface of the water, the struts, blades and lift forces being so correlated that when the hull is flying, the interspacing between the points where the blades pierce the waltler is substantially. equal to double the beam of the hu 6. A hydrofoil system comprising a hull, power means for propelling said hull, a pivot shaft mounted on each side of the forward portion of said hull, a strut depending from each of said shafts for swinging movement transversely of said hull between inner and outer positions respectively corresponding to the floating and flying positions of said hull, lift surfaces secured to the lower end portion of each of said struts, said lift surfaces including a swept-back hydrofoil blade extending outward from said strut and a swept-back brace having a cross-sectional shape approximating that of said hydrofoil blade, said brace extending rearward from the strut adjacent said pivot shaft to the end portion of said hydrofoil blade, the brace and hydrofoil blade being within the plan profile of the hull when the strut is in said inner position and the hull is floating, and said hydrofoil blade being in surface-piercing relation to the water when the hull is flying.

7. A hydrofoil system comprising a hull, power means for propelling said hull, a pivot shaft mounted on each side of the forward portion of said hull, a strut depending from each of said shafts for swinging movement transversely of said hull between inner and outer positions respectively corresponding to the floating and flying positions of said hull, lift foils secured to the lower end of each of said struts, the lift foils associated with each strut including a swept-back hydrofoil blade extending outward from the strut and a swept-back tip foil extending inward from the strut, and a swept-back brace having a cross-sectional shape approximating that of a hydrofoil blade and extending rearward from each strut to the end portion of the associated hydrofoil blade, the brace, blade and tip of each strut being within the plan profile of the hull when said struts are in said inner positions and the hull is floating, said outwardly extending hydrofoil blades being in surface-piercing relation to the water when the hull is flying.

8. A hydrofoil system according to claim 7 wherein said hydrofoil blade and said tip foil are non-planar, and in which the tip foil has less positive dihedral than the hydrofoil blade when the associated strut is in said outer position.

9. In a hydrofoil craft, a hull, hydrofoil units adapted to support said hull; each of said hydrofoil units including an upright uncambered base ventilated strut and a base vented hydrofoil blade extending away from said strut, said blade having a swept back trailing edge merging with the trailing edge of said strut so that the propagation of atmospheric air, in the trailing edge voids rearward of said strut and said blade, is downward along the strut and thence upward and outward along said blade.

10. A hydrofoil construction according to claim 9 wherein the trailing edge surfaces of said strut and said blade meet in a flush juncture to provide minimum resistance to the flow of air outward along the trailing edge of said blade.

11. In a hydrofoil craft, a hull; port and starboard hydrofoil units adapted to support said hull; each of said hydrofoil units including an upright uncambered base ventilated strut, and a base ventilated hydrofoil blade having a swept back trailing edge and projecting outward and upward from its juncture with the associated strut in piercing relation to the surface of the water; the propagation of atmospheric air in the trailing edge voids rearward of said strut and said blade being downward along the upright uncambered strut and thence upward from the lower portion of the strut along said trailing edge of said hydrofoil blade to the surface, due to the sweepback of the trailing edge of said blade, so as to prevent the influx of air from the surface downward in the void trailing said hydrofoil blade.

12. In a hydrofoil craft, a hull; a hydrofoil unit adapted to support said hull; said hydrofoil unit including an upright base ventilated strut having zero camber and a trailing edge with substantially no sweepback, and a base vented hydrofoil blade having a submerged portion extending upward from said strut in diagonal piercing relation to the surface of the water when the hull has sufiicient forward speed to develop lift in said blade, said blade having a swept back trailing edge so that the propagation of atmospheric air in the trailing edge voids rearward of said strut and said blade is downward along the base of said strut and thence upward from the lower portion of the strut along said hydrofoil blade to the surface.

13. A hydrofoil craft comprising a hull, depending fore and aft hydrofoil units secured to said hull, each of said units including an upright strut mounted on the hull, a foil blade mounted on each strut with its trailing edge substantially coplanar with the trailing edge of said strut at the intersection of the lift foil and strut, each of said blades being at least part of the time in piercing relation to the surface of the water and having a trailing edge swept back from the trailing edge of the associated strut, said blades and struts both having base ventilated profiles whereby the voids adjacent said trailing edges are vented by atmospheric air travelling down the rear of the struts and outward along the trailing edges of the blades toward the surface of the water.

14. A method of forming a hydrofoil blade which is to have a varying mean camber through its length comprising the steps of forming an elongate blank having a uniform width between its leading and trailing edges, and having a uniform cross-sectional lift foil shape and a constant camber throughout its length; and trimming the trailing edge portion of the blade lengthwise along a line diagonally related to its longitudinal edges so that the blank is longitudinally tapered and the resulting blade has a varying mean camber.

15. A method of forming a base ventilated hydrofoil blade having uniformly varying camber, chord and angle of attack comprising the steps of forming a blade extrusion having a predetermined cross sectional shape and length, and having a uniform width equal to the maximum desired chord of the finished blade, said blade extrusion thus initially defining a lift blade having a narrow leading edge, a blunt trailing edge, and end profiles of identical shape; and tapering the blade between said ends by severing the extrusion along a line extending along one surface of the blade between points located at the intersection of said surface with the trailing edge of the blade at its desired ultimate points of maximum and minimum chord.

16. An anti-cavitation hydrofoil system comprising a hull; an elongate surface-piercing strut depending from said hull, said strut having a tapered leading edge and a blunt trailing edge which is wider than the major crosssectional thickness of the strut; and a surface-piercing swept back hydrofoil blade rigidly secured intermediate its ends to the lower end of said strut, said blade having positive dihedral, a cambered upper surface and a blunt trailing edge, said trailing edge being substantially coincident with the trailing edge of said strut and wider than the major cross-sectional thickness of the blade.

References Cited UNITED STATES PATENTS 1,852,680 4/1932 Shaw 11466.6 2,713,317 7/1955 Herz 11466.6 2,984,197 5/1961 Bader 114-666 3,109,495 11/1963 Lang 114-666 3,164,116 1/1965 Lopez 11466.6 3,183,871 5/1965 Reder 11466.6 3,191,567 6/1965 Ask 11466.6 3,211,119 10/1965 Kiekhaefer 114-665 OTHER REFERENCES Ser. No. 268,421, 0. Tietjens (A.P.C.), published May 1943.

ANDREW H. FARRELL, Primary Examiner.

MILTON BUCHLER, Examiner. 

1. A HYDROFOIL CRAFT COMPRISING A HULL INCLUDING UPRIGHT SIDE WALLS, A PIVOTABLE HYDROFOIL UNIT AT EACH SIDE OF THE HULL, MEANS CONNECTED TO SAID HULL AND DEFINING A PIVOT AXIS FOR EACH HYDROFOIL UNIT INWARDLY OF SAID UPRIGHT SIDE WALL, AND MEANS FOR SWINGING AND HYDROFOIL UNIT ABOUT SAID AXIS BETWEEN AN OUTER POSITION IN WHICH SAID UNIT HAS PORTIONS PROJECTING OUTWARDLY BEYOND THE PLANE PROFILE OF SAID HULL, AND AN INNER POSITION IN WHICH SAID UNIT LIES TOTALLY WITHIN SAID PLAN PROFILE BENEATH SAID HULL AND INWARD OF SAID SIDE. 